此段地层采用牙轮（刀）头钻进。
牙轮钻机钻凿的岩层是随机分布、错综复杂的，因而钻进过程难以定义。
The rock stratum drilled by a rotary drill is random distributed and complicated, so it is difficult to define the drilling process.
在牙轮钻头的钻进中，水射流是钻进速度快慢的决定因素之一。
Water jet flow is one of the decisive factors for drilling rate during rock bit drilling.
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